System for testing hearing



Dec. 12, 1950 Filed Nov. 2'7, 1946 B. M. HARRISON SYSTEM FOR TESTINGHEARING 2 Sheets-Sheet 1 5 FIG. I

mmvroa. BERTRAM M. HARRISON HIS ATTORNEY Dec. 12, 1950 B. M. HARRISONSYSTEM FOR TESTING HEARING Fild Nov. 27, 1946 2 Sheets-Sheet 2 FIG. 3

INVENTOR. BERTRAM M. HARRISON BY WWW HIS ATTORNEY Patented Dec. 12, 1950UNITED STATES PATENT OFFICE 2 Claims.

The present inventionrelates to a device for testing and analyzing thehearing response of individuals, particularly for the purpose ofdetermining the utility, nature, and character of hearing aids which maybe required by the individual. The present method of analysis applies toindividuals who may use hearing aids of the bone or air conduction type.

It has been observed that an individual who is hard of hearing willoften hear certain tones much more readily than other tones and effortshave been made to determine the so-called hearing characteristics orhearing curve of the individual over the normal range of audiblefrequencies. A determination of these factors greatly aids in the designof the type of apparatus to be used, particularly in showing whatfrequencies should be amplified greater in in tensity than others. Thedetermination of such an individual characteristic or frequency curve isnot a simple matter and in the methods and systems which have been used,unavoidable errors or mistakes occur for a number of reasons, dependingeither upon the individuals observation or response to questions askedby the doctor or examiner. oftentimes a patient may state that he canhear a sound well when he hears it poorly or not at all. This may bedone unwittingly or willfully, but in either event it hampers theobserver in providing the proper type of hearing aid. The same situationalso applies to comparison of sounds on an intensity basis. Asking theobserver to express an opinion or to make a choice is not alwaysreliable in providing true results.

In the present invention, the method and system employed in such thatthe patient must make his selection and observation in such a mannerthat there will be little chance for deception, either knowingly orunknowingly, by him. In each case the patient makes his own observationwithout the aid or assistance of the observer, and then the observer, bysimple comparison with electrical apparatus, determines how far off thepatient has been. This method of study is particularly useful indeterminin the frequency characteristic curve of the patient, i. e., thecurve which gives an indication of the patients ear sensitivity atdifferent frequencies.

In the present invention, the patient is required to tune an oscillatorproducing a pure acoustic vibration to the frequency of a givenoscillator, both oscillators preferably being of substantially the sametone intensity. The patient will be able under normal conditions toobtain a close tuning, I have determined, where his hearing isrelatively good. Where, however, he has diiiiculty in hearing, i. e.,hearing sounds of a certain pitch or frequency, his ability to adjustthe tone to a given tone materially decreases. The measure by which heis off frequency is a good and fair indication of his relativeinsensitivity for the particular frequency. In order to make the run oftests complete, it may be necessary to make observations with thepatient first at a given tone volume of the test note, and then at lowertone volumes, depending upon the ability of the patient to hear. If thepatients ears are very bad, observations must necessarily be made with ahigher constant volume, whereas if the patient has hearing below normalbut not exceeding poor, a lower volume signal or tone may be used.

The present invention will be more fully described in connection withthe apparatus illustrated in the drawings which form a part of theinvention and by means of which the method of the present invention maybe carried out.

In the drawings,

Fig. 1 shows schematically a circuit used in the present invention;

Fig. 2 shows a more complete system embodying the same principles of theinvention as set forth in Fig. 1; and

Fig. 3 shows a still further modification of the system in accordancewith the present invention by which the method thereof may be carriedout.

In Fig. 1, the individual under test may be seated before the oscillatorl with one or a pair of head phones 2 on his cars. If desired, each earmay be tested separately by using only a single phone or by using a pairof phones or bone conduction transducerswith a switch which may cut inthe right or left ear, whichever is desired. The patient under test hasreadily available the control knob 3 for adjusting the frequency of theoscillator I. A second oscillator 4 is provided which is under thecontrol of the observer by means of the knob 5. The output of bothoscillators l and 4 may be connected in parallel by means of the line 6across which the head phones 2 are connected through a volume control Iand a volume meter 1 reading in decibels or the like, for regulating thevolume of the oscillator heard in the head phones. The oscillators l and4 produce a substantially pure or sinusoidal note so that no difficultyis encountered with multiple frequencies which often go to make up thecharacter of musical instruments. A keying switch 8 is provided for useeither by the patient or ob server. This key may comprise a single poledouble throw switch so that in its upper position, as viewed in Fig. 1,the sounds of oscillator I will be impressed across the head phones,while when the key is in its lower position the sounds of oscillator 4will be impressed across the head phones.

In the making of observations or tests on the patient, the calibratedoscillator 4 may be set at a definitely chosen frequency and the volumecontrol I may also be adjusted to a desired volume control position. Thepatient is then asked to adjust the oscillator I to the same frequencyas the oscillator 4. He does this by turning the knob on the oscillatorI and then throwing the key 8 up and then down to compare the note heardfrom the oscillator I with the note heard from the oscillator 4. The key8 is so arranged that sounds of only one of the oscillators may be heardata time. When the patient has made his setting, the observer willdeduct the frequencies indicated. on the two calibrated oscillators Iand4 to get the difference or error frequency. He may also, if desired,listen to the 1..

beat note by throwing the switch 9, in which case both oscillators willbe heard together.

The operator may desire to test the patient at a high volume, in whichcase the potentiometer or volume control I is adjusted to permit acomparatively loud sound to be heard on the head phone .2. The volumecontrol .meter 1 may, of course, be calibrated in acoustic or electricalunits and should be associated witheach observation curve made on theindividual under test. It

For instance, if a curve is taken with the volume control in a givenposition, this curve should be marked for the particular volume settingat which it was taken. It has been found that with a louder volume, apatient may be more able to adjust frequencies than with a lower volume,and, in fact, the most useful results are usually obtained when thevolume is low enough so that the patient has some difiiculty over theentire frequency range but yet not so low but that observations can bemade over the whole range.

In the form shown in Fig. 2 the same elements as used in Fig. 1 areincluded, with the addition, however, of a mixer stage III, a doublepole double throw selector switch I I and a frequency indicator I2 towhich the output of the mixer is connected. This modification is chieflyfor the use of the operator. The patient, as before, will use the headphones with the switch I I thrown in the downward position. When he hasmade asetting, the operator will throw the switch II upward, connectingthe output of oscillators I and t to the mixer, where the beat frequencywill be created, which frequency will be indicated on the frequencyindicator I2. In this way, a ready indication of the frequencydifference between the oscillators i and 4 may be obtained.

In the circuit shown in Fig. 3, three oscillators A, B, and C may beused, the oscillator B being chiefly used as a constant frequency sourcewhile the oscillator A is controlled by the patient and C,-by theobserver. The output of each oscillator, which may be of any usual wellknown type, is fed to the corresponding amplifier A, B or C.

In this circuit, there is further provided a gang switch I3 operable bya single mechanism, which gang switch controls seven .independent singlesections I, 2, 3, 4, 5', 6', and 8. The gang switch is under the controlof the observer. Besidesthe elements previously described, there .is

also included in the system a mixer stage I4, the purpose of which is tomix the output of the amplifiers A and B, or B and C, or A and C. Theoutput of the mixer stage may be connected to a low pass filter I5,which acts as the intermediate element in the circuit, which ends withthe audio amplifier I1 provided with a volume control I8.

The gang switch in its upper position In as indicated in Fig. '3connects the oscillators A and C in parallel to the grid I9 of the mixerstage, while the oscillator B is connected to the grid of the mixerstate. Oscillators A andC however in this setting, as in Figs. 1 and 2,are not used simultaneously by the patient, but are alternately selectedby means of the key 2|. When the key is in its upper position,oscillator A is selected, and when the key is in its lower position,oscillator C is selected. In the arrangement of Fig. 1, the note whichthe patient and the operator both hear is the beat frequency between theoscillators .A and B or the oscillators B and C, depending upon theposition of the switch -2-I. Since oscillator B is set at a constantfrequency and oscillator C is set by the observer, oscillator A must beset by the patient to match the frequency beat between the oscillators Band C. The head phones 22 are used by the patient. The volume to thephones is of course controlled by the volume control I8, which ispreferably calibrated, so that for any desired run over the frequencyrange the volume may be maintained at a definite intensity. The low passfilter I5 may be used to purify the oscillator note, if that isnecessary. I

The patient will make an observation with the gang switch set in theposition indicated in Fig. 3. If the gang switch position is changed sothat its switch arms are in position 20, the oscillator A and itsamplifier will be connected to the grid I9 while that of oscillator Cwill be connected to the grid 20. In this position, the oscillator B byvirtue of section 9 will be out of circuit. The position of the sections5 and 6 of the gang switch .in the second position short circuits thekey 2!, thus preventing either oscillator A or B from being disconnectedfrom the mixer circuit. This enables the two oscillators A and B, byestablishing a zero beat note, to be set at the identical frequency ofoscillation. The amount of readjustment necessary to accomplish this isa measure of the error made by the patient.

A further position of the gang switch throws the oscillators A and C onpairs of plates of a cathode ray tube such that a visual observation offrequency identity may be obtained. In this case, the switch '8 cuts outthe constant condenser 38 and throws into circuit the condenser 3I whichhas a range of from 0 to double the value of the constant condenser sothat tuning of the oscillator C in both directions may be accomplishedwith respect to the oscillator A. In this way, whatever change infrequency may take place between oscillators A and C, the twooscillators may be tuned again to the same frequency. Condenser 3Icarries a calibrated dial 32 so that reading of its setting at zero beatindicates the number of cycles error made by the patient.

Afrequency sensitive voltmeter 3d maybe con nected in circuit across thephones 22 to measure the intensity level of the signal heard in thephone. This intensity level may be maintained constant for a frequencyrun and varied for successive runs.

I claim: 1. A system for testing an individual for de fective hearingcomprising a pair of oscillators for independently producing notes ofdesired frequency, means under control of the individual under test forvarying the frequency of one oscillator in accordance with the sound hehears to match that of the other, means under control of the tester forchanging the frequency of the other oscillator to the desired pitchwhich the individual is to match, listening phones connected to bothoscillators, a switching means for selectively operating one or theother oscillator, and a switching means for operating both oscillatorssimultaneously.

2. A system for testing an individual for defective hearing comprising apair of oscillators for independently producing notes of desiredfrequency, means under control of the individual under test for varyingthe frequency of one oscillator in accordance with the sound he hears tomatch that of the other, means under control of the tester for changingthe frequency of the other oscillator to the desired pitch which theindividual islto match, listening phones connected to both oscillators,a switching means for selectively operating one or the other oscillator,and a switching means for operating both oscillators simultaneously,said latter being under control of the tester.

BERTRAM M. HARRISON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,528,774 Kranz Mar. 10, 19252,217,394 Wengel Oct. 8, 1940 2,235,733 Witting Mar. 18, 1941 2,416,353Shipman et a1 Feb. 25, 1947

